I replaced the real domain with example.com
It's safe to assume the server is connected to the internet via a Time Warner business connection?
Most likely it's because rd-proto2.example.com does not exist in public DNS and your email is coming From: that domain name.
Try forcing the email to come From:
username@example.com and this part of the relay problem should be fixed.
What command is creating the emails? Sometimes web based applications try to send as apache@localhost, something like that could be the problem too.
What is in your postfix logs for this email before you get the error message?
Also, if this is an environment with several servers, consider adding an outgoing smtp relay, and a custom PTR for the outgoing mail IP such as smtp.example.com.
Over the long haul you should have better results running your own relay than relying on ISP smtp relays.